1. Field of the Invention
This invention relates to a light-receiving/emitting composite unit, a method for manufacturing the same, and a displacement detection device for detecting a relative shift position of a moving part of a machine tool, a semiconductor manufacturing device or the like.
This application claims priority of Japanese Patent Application Nos. 2002-127525, 2002-127526 and 2002-127527, file on Apr. 26, 2002, the entireties of which are incorporated by reference herein.
2. Description of the Related Art
Conventionally, an optical displacement detection device using a diffraction grating has been known as a device for detecting a relative shift position of a moving part of a machine tool, a semiconductor manufacturing device or the like.
For example, FIGS. 1 and 2 show a conventional optical displacement measuring device proposed in the Japanese Publication of Laid-Open Patent Application No. S60-98302. FIG. 1 is a perspective view schematically showing this conventional optical displacement measuring device 100. FIG. 2 is a side view schematically showing this conventional optical displacement measuring device 100.
The conventional optical displacement measuring device 100 has a diffraction grating 101 which linearly moves in the directions of arrows X1 and X2 in FIGS. 1 and 2 along with the movement of a moving part of a machine tool or the like, a light source 102 for emitting light, a half mirror 103 for splitting the light emitted from the light source 102 into two beams and superposing two diffracted light beams from the diffraction grating 101 to cause interference, two mirrors 104a, 104b for reflecting the diffracted light beams diffracted from the diffraction grating 101, and a photodetector 105 for photoelectrically converting the two diffracted light beams interfering with each other and thus generating an interference signal.
The light emitted from the light source 102 is split into two beams by the half mirror 103. These two beams are cast on the diffraction grating 101. Each of the two beams cast on the diffraction grating 101 is diffracted by the diffraction grating 101 and becomes diffracted light (hereinafter this diffracted light is referred to as first-time diffracted light). This first-time diffracted light is reflected by the mirrors 104a, 104b. The first-time diffracted light reflected by the mirrors 104a, 104b is cast again on the diffraction grating 101 and diffracted again (hereinafter this re-diffracted light referred to as second-time diffracted light). The two second-time diffracted light beams become incident on the half mirror 103 through the same optical path, then superposed to interfere with each other, and cast on the photodetector 105.
In such a conventional optical displacement measuring device 100, displacement of the diffraction grating 101 in the directions of arrows X1 and X2 in FIGS. 1 and 2 can be detected. Specifically, in the optical displacement measuring device 100, a phase difference is generated in the two second-time diffracted light beams from the diffraction grating 101 in accordance with the movement of the diffraction grating 101. Therefore, this optical displacement measuring device 100 can measure the shift position of a moving part of a machine tool or the like by detecting the phase difference between the two second-time diffracted light beams from an interference signal provided from the photodetector.
FIGS. 3 and 4 show another conventional optical displacement measuring device proposed in the Japanese Publication of Laid-Open Patent Application No. H60-98302. FIG. 3 is a perspective view schematically showing a conventional optical displacement measuring device 110. FIG. 4 is a side view schematically showing the conventional optical displacement measuring device 110.
The conventional optical displacement measuring device 110 has a diffraction grating 111 which linearly moves in the directions of arrows X1 and X2 in FIGS. 3 and 4 along with the movement of a moving part of a machine tool or the like, a light source 112 for emitting light, a half mirror 113 for splitting the light emitted from the light source 112 into two beams and superposing two diffracted light beams from the diffraction grating 111 to cause interference, two first mirrors 114a, 114b for casting the two beams split by the half mirror 113 at the same position on the diffraction grating 111, two second mirrors 115a, 115b for reflecting the diffracted light beams diffracted from the diffraction grating 111, and a photodetector 116 for receiving the two diffracted light beams interfering with each other and thus generating an interference signal.
The light emitted from the light source 112 is split into two beams by the half mirror 113. These two beams are reflected by the first mirrors 114a, 114b, respectively, and cast at the same position on the diffraction grating 111. Each of the two beams cast on the diffraction grating 111 is diffracted by the diffraction grating 111 and becomes first-time diffracted light. This first-time diffracted light is reflected by the second mirrors 115a, 115b. The first-time diffracted light is cast again on the diffraction grating 111 and diffracted to become second-time diffracted light. The two second-time diffracted light beams become incident on the half mirror 113 through the same optical path, then superposed to interfere with each other, and cast on the photodetector 116.
In such a conventional optical displacement measuring device 110, displacement of the diffraction grating 111 in the directions of arrows X1 and X2 in FIGS. 3 and 4 can be detected. Specifically, in the optical displacement measuring device 110, a phase difference is generated in the two second-time diffracted light beams from the diffraction grating 111 in accordance with the movement of the diffraction grating 111. Therefore, this optical displacement measuring device 110 can measure the shift position of a moving part of a machine tool or the like by detecting the phase difference between the two second-time diffracted light beams from an interference signal provided from the photodetector 116.
However, in the manufacturing process, it is necessary to assemble the above-described conventional optical displacement measuring devices 100 and 110 while adjusting the separately manufactured individual optical components. Therefore, precise adjustment is required with respect to unevenness in accuracy of completion and characteristics of each component, and the process is complicated. Moreover, the device lacks stability with the lapse of time and reduction in size and weight of the whole device is obstructed.
The polarization axis of the light emitted from the light source must be adjusted to an angle at which the light is distributed at a ratio of one to one by the half mirrors 103, 113. Therefore, a more complicated process must be introduced and an excessive space is necessary in the device.
Moreover, in the manufacturing process, it is necessary to assemble the above-described conventional optical displacement measuring devices 100 and 110 while adjusting the separately manufactured individual optical components. Therefore, precise adjustment is required with respect to unevenness in accuracy of completion and characteristics of each component. A complicated process must be introduced, thus obstructing reduction in price.
As a large space is necessary for adjusting, fastening and fixing the components, miniaturization of the whole device cannot be realized.
Furthermore, since an adhesive must be used for fixing the components, the adhesive state changes depending on the environmental changes, and a deviation between the components may occur because of the environmental changes and changes with the lapse of time.
Meanwhile, when a difference occurs in the optical path lengths of the two beams split by the above-described half mirror 113, a phase change occurs, causing a measurement error. Therefore, in the optical displacement measuring device 100 and 110, the optical path lengths of the above-described two split beams must be adjusted to be equal in order to realize desired characteristics.
FIG. 5 shows a conventional optical displacement measuring device in which the optical path length of the split beams can be adjusted to be equal, proposed in the Japanese Publication of Laid-Open Patent Application No. S61-83911.
This conventional optical displacement measuring device 120 has a diffraction grating 121 which linearly moves in the directions of arrows X1 and X2 in FIG. 5 along with the movement of a moving part of a machine tool or the like, a light source 122 made of a multi-mode semiconductor laser for emitting light, a half mirror 123 for splitting the light emitted from the light source 122 into two beams and superposing two diffracted light beams from the diffraction grating 121 to cause interference, two mirrors 124a, 124b for reflecting the diffracted light beams diffracted from the diffraction grating 121, a half mirror 125 for separating the diffracted light beams interfering with each other, and photodetectors 126a, 126b for photoelectrically converting these diffracted light beams to generate an interference signal.
The light emitted from the light source 122 is split into two beams by the half mirror 123. These two beams are cast on the diffraction grating 121. Each of the two beams cast on the diffraction grating 121 is diffracted by the diffraction grating 121 and becomes first-time diffracted light. The first-time diffracted light is reflected by the mirrors 124a, 124b. The first-time diffracted light is cast again on the diffraction grating 121 and diffracted to become second-time diffracted light. The two second-time diffracted light beams become incident on the half mirror 123 through the same optical path, then superposed to interfere with each other, and cast on the photodetectors 126a, 126b via the half mirror 125.
In such a conventional optical displacement measuring device 120, since a multi-mode semiconductor laser is used as the light source, displacement of the diffraction grating 121 in the directions of arrows X1 and X2 in FIG. 5 can be detected while the optical path lengths of the split beams can be controlled. That is, in this optical displacement measuring device 120, since the difference in optical path length can be detected, precise adjustment of the optical path length can be realized. Moreover, since the adjustment state can be monitored, an error based on a change in wavelength can be easily identified.
Meanwhile, in the above-described optical displacement measuring devices 100 and 110, position detection is difficult when rotational shift in the directions of arrows A1 and A2 and rotational shift in the directions of arrows B1 and B2 occur, as shown in FIGS. 1 to 4. To prevent the influence of such changes in angle of the diffraction grating, another optical displacement measuring device is proposed, for example, in the Japanese Publication of Laid-Open Patent Application No. 2000-81308.
This conventional optical displacement measuring device 130 has a diffracting grating 131 which is mounted on a moving part of a machine tool or the like and linearly moves, a light source 132 for emitting light, a light-receiving element 133 for receiving two second-time diffracted light beams Lc1, Lc2 interfering with each other and thus generating an interference signal, a position detecting unit 134 for detecting a shift position from the diffraction grating 131 on the basis of the interference signal from the light-receiving element 133, an irradiation light-receiving optical system 135 for splitting light La emitted from the light source 132 into two beams La1, La2 and casting the two beams on the diffraction grating 131 and for causing the second-time diffracted light beams Lc1, Lc2 from the diffraction grating 131 to interfere with each other and casting these second-time diffracted light beams on the light-receiving element 133, and a reflection optical system 136 for reflecting two first-time diffracted light beams Lb1, Lb2 from the diffraction grating 131 and casting these first-time diffracted light beams again on the diffraction grating 131, as shown in FIG. 6.
The irradiation light-receiving optical system 135 has a first image-forming element 141 for causing image formation of the light La emitted from the light source 132 onto the lattice plane of the diffraction grating 131, a half mirror 142 for splitting the light La emitted from the light source into the two beams La1, La2 and superposing the two second-time diffracted light beams Lc1, Lc2 from the diffraction grating 131 to cause interference, a reflector 143 for reflecting the light beams La1, La2 split by the half mirror 142 and reflecting the second-time diffracted light beams Lc1, Lc2, and a second image-forming element 144 for causing image formation of the two second diffracted light beams Lc1, Lc2 superposed by the half mirror 142 onto the light-receiving surface of the light-receiving element 133.
The reflection optical system 136 has reflectors 146 for reflecting the first-time diffracted light beams Lb1, Lb2 generated from the light beams La1, La2 and casting the first-time diffracted light beams again on the diffraction grating 131, and third image-forming elements 148 for collimating the first-time diffracted light beams Lb1, Lb2 generated from the light beams La1, La2 and casting the collimated light beams on the reflectors 146.
In the optical displacement measuring device 130 of the above-described structure, as the diffraction grating 131 shifts in a direction X1 or X2 in accordance with the movement of the moving part, a phase difference is generated between the two second-time diffracted light beams Lc1, Lc2. In this optical displacement measuring device 130, the two second-time diffracted light beams Lc1, Lc2 are caused to interfere with each other and an interference signal is detected. The phase difference between the two second-time diffracted light beams Lc1, Lc2 is found from the interference signal and the shift position of the diffraction grating 131 is detected.
Moreover, in this optical displacement measuring device 130, the first image-forming element 141 causes image formation of the light La emitted from the light source 132 on the lattice plane of the diffraction grating 131 and the third image-forming elements 148 collimate the first-time diffracted light beams Lb1, Lb2 and constantly cast the collimated light beams perpendicularly to the reflectors 146. Therefore, the first-time diffracted light beams Lb1, Lb2 reflected by the reflectors 146 necessarily return on the same optical paths as in the case of incidence and become incident on the same point of incidence on the lattice plane of the diffraction grating 131, even when their optical axes are deviated from each other. Therefore, in this optical displacement measuring device 130, even when the diffraction grating 130 is inclined, the second-time diffracted light beams Lc1, Lc2 necessarily pass the same optical paths as in the case of incidence. There is no change in their optical path lengths.
However, the optical displacement measuring device 120 using a multi-mode semiconductor laser as the light source, proposed in the Japanese Publication of Laid-Open Patent Application No. S61-83911, has a problem that a general semiconductor laser cannot be used, though the device can control the optical path length with respect to changes in wavelength of the light source and thus can realize stable characteristics. Moreover, the optical displacement measuring device 120 cannot deal with changes in angle of the diffraction grating and has a problem that allowable errors are limited not only at the time of actually mounting the components constituting the device but also at the time of mounting the diffraction grating on the moving part.
In the optical displacement measuring device 130 proposed in the Japanese Publication of Laid-Open Patent Application No. 2000-81308, which reduces the influence of changes in angle of the diffraction grating, an image-forming element such as a lens must be used for realizing angle adjustment of the optical path and the structure of the device is complicated. Moreover, since this optical displacement measuring device 130 uses individual components such as lenses and half mirrors, the device lacks stability with the lapse of time and miniaturization of the device is seriously obstructed.